Normoglycemia in diabetic patients is controlled by the injection of insulin into the body of the patient. Insulin injections several times a day are required, although more recently long lasting ultralente and protamine zinc insulin has decreased the frequency of injection for some diabetics to once every day.
There is a need for a system which would permit the administration of one large dose of insulin at widely-spaced intervals of weeks or even months. Such a large dose would need to be associated with some means of permitting the administered insulin to be released into the blood stream over a long period of time, so as to be effective over that period.
It has previously been suggested in European Patent Publication No. 0,054,396, published June 23, 1982, to provide implants, microbeads and microcapsules suitable for injection into an animal body comprising cross-linked but physically-native albumin and a non-albumin substance, such as, a steroid or an enzyme. Upon injection or implantation into an animal body, the non-albumin substance contained therein is released slowly as the cross-linked albumin is slowly dissolved by biodegradation.
Although this prior art publication does not mention insulin as a potential non-albumin substance, superficially this prior art approach would seem promising for the production of long term insulin release. When the cross-linking procedure which is described in the prior art publication using glutaraldehyde, is attempted to be used in conjunction with insulin as the non-albumin substance, the resulting product is ineffective in decreasing blood sugar levels upon injection or implantation in a body.